Dynamic punching shear failure of a RC flat slab-column connection under a collapsing slab impact

Abstract

Reinforced concrete flat slabs are very common in residential and office buildings construction. The sensitivity of the flat slab-column connection to punching shear is well known and standards include design rules to ensure the connection safety under static loading. Such failures may occur due to static excessive loading or when buildings are subjected to an extreme event; in such cases, the local failures of the column-slab connections, are followed by the slab collapse downward. The collapsing slab then impacts the slab underneath, and this collision event is critical to the building safety. It may cause dynamic punching shear failure to the impacted slab and initiate a progressive collapse process of the slabs underneath, or it may be arrested by the first impacted slab. This scenario of impact between the two slabs is in the focus of this paper, disregarding the cause of the first slab failure. In this study, the problem is modelled by a representative part of a slab resting on a column; the slab is analyzed under to the impact action of a similar collapsing slab from above. A corner non-symmetrical part of the slab has been selected to represent the more general non-symmetrical conditions of the problem. Many studies have been done on the connection behavior under static loading, but relatively little has been done on the impact shear response of RC column-slab connections despite the major importance of this issue and its relevance to the integrity of the entire building. The behavior of this connection depends on many parameters, and mainly on its longitudinal and shear reinforcements. This paper presents the numerical detailed simulations of a connection under impact conditions, and studies the dynamic response of the RC column-slab connection due to the impact of a falling upper-level slab. The analysis has been performed on slabs with longitudinal reinforcement with (or without) additional shear reinforcement. The paper examines the effects of several major parameters such as the upper slab's falling height, the slab dimensions, the shear reinforcement, and the reinforcement ductility on the column-slab connection behavior and the type of its failure. This paper provides new insight on the impact scenario, the slabs response and the details of the resulting damage.